CentralHeatPumpSystem-CentralChillerHeaterSystem_Cooling_Heating.idf

[Helarga]

For the CentralChillerHeaterSystem_Cooling_Heating.idf, the simulation time period is set for two days ( heating and cooling), during the heating day, the evaporator heat flow rate is higher than the condenser heat flow rate. While results during the cooling day are reasonable.

I have highlighted the results at the attached excel sheet., ( from row:423) CentralChillerHeaterSystem_Cooling_Heating.xlsx

energyPlus 9.1

[mitchute]

This appears to be a legitimate issue, but I'm not sure how we should proceed.

The condenser load is being set properly here:

https://github.com/NREL/EnergyPlus/blob/2b65de010cfe6ad6d80957f92b616b0032cffb04/src/EnergyPlus/PlantCentralGSHP.cc#L2509

But then a few lines later is being adjusted based on the heating load.

https://github.com/NREL/EnergyPlus/blob/2b65de010cfe6ad6d80957f92b616b0032cffb04/src/EnergyPlus/PlantCentralGSHP.cc#L2516

And then finally, set again based an energy balance

https://github.com/NREL/EnergyPlus/blob/2b65de010cfe6ad6d80957f92b616b0032cffb04/src/EnergyPlus/PlantCentralGSHP.cc#L2535

which is based on a condenser delta T that was set based on a user-specified condenser temperature and the condenser inlet temperature

https://github.com/NREL/EnergyPlus/blob/2b65de010cfe6ad6d80957f92b616b0032cffb04/src/EnergyPlus/PlantCentralGSHP.cc#L2260-L2261

Regardless of whether the condenser heat is being used for heating or dumped to sink, it still has to pass through the condenser, so all of this adjusting the condenser load based on external conditions doesn't make sense from the perspective of the refrigeration cycle. That sort of accounting should be handled later.

I'll keep digging...

[Helarga]

This appears to be a legitimate issue, but I'm not sure how we should proceed.

The condenser load is being set properly here:

https://github.com/NREL/EnergyPlus/blob/2b65de010cfe6ad6d80957f92b616b0032cffb04/src/EnergyPlus/PlantCentralGSHP.cc#L2509

But then a few lines later is being adjusted based on the heating load.

https://github.com/NREL/EnergyPlus/blob/2b65de010cfe6ad6d80957f92b616b0032cffb04/src/EnergyPlus/PlantCentralGSHP.cc#L2516

And then finally, set again based an energy balance

https://github.com/NREL/EnergyPlus/blob/2b65de010cfe6ad6d80957f92b616b0032cffb04/src/EnergyPlus/PlantCentralGSHP.cc#L2535

which is based on a condenser delta T that was set based on a user-specified condenser temperature and the condenser inlet temperature

https://github.com/NREL/EnergyPlus/blob/2b65de010cfe6ad6d80957f92b616b0032cffb04/src/EnergyPlus/PlantCentralGSHP.cc#L2260-L2261

Regardless of whether the condenser heat is being used for heating or dumped to sink, it still has to pass through the condenser, so all of this adjusting the condenser load based on external conditions doesn't make sense from the perspective of the refrigeration cycle. That sort of accounting should be handled later.

I'll keep digging...

Hi Matt, Thanks a lot!

[Myoldmopar]

This does look legitimately wrong. The component shouldn't be just overwriting the condenser energy. My guess is that the whole section where it alters the value of condenser energy needs to be rearranged so that it acts as a passive device rather than actively trying to meet a condenser "load". It should just calculate the delta temp based on flow and Q or calculate the flow based on delta temp and Q, and in either case, add the Q to the condenser side. I think I understand in this configuration, the condenser side is actually going to the supply side of a loop to reuse the heat, but it should be a more passive component, like a GLHE, or a waterside economizer.

@rraustad or @mjwitte perhaps one of you know a little more about these components in real life and can comment on what they would actually do with their evaporator and condenser energy rates. They can't control both to specified control values.

[mjwitte]

I have no experience with these.

[RKStrand]

Note: this issue appears to be the same as the first of two issues noted in Defect #10065. See the conversation in that defect for more, updated information.